The present invention relates to a semiconductor module,                wherein the semiconductor comprises a substrate made from an electrically insulating material,        wherein a structured metal layer, via which at least one electrical component is contacted, is applied to a top side of the substrate,        wherein the structured metal layer is applied to the substrate only in a central region of the substrate such that an edge region surrounding the central region and in which the structured metal layer is not applied to the substrate is left on the top side of the substrate,        wherein a contact layer for contacting a cooling body and which is situated opposite the structured metal layer is applied to a bottom side of the substrate in the central region.        
Semiconductor modules of this type are generally known. Reference can be made, for example, to US 2016/0 021 729 A1.
A semiconductor module is known from US 2009/0 213 546 A1 which comprises a substrate made from an electrically insulating material. A structured metal layer, via which at least one electrical component is contacted, is applied to a top side of the substrate. The structured metal layer is applied to the whole top side. A contact layer for contacting a cooling body is applied to a bottom side of the substrate, essentially coinciding with the structured metal layer.
A semiconductor module is known from US 2014/0 204 533 A1 which comprises a substrate made from an electrically insulating material. A structured metal layer, via which at least one electrical component is contacted, is applied to a top side of the substrate. The structured metal layer appears to be applied to the substrate only in a central region of the substrate such that an edge region surrounding the central region and in which the structured metal layer is not applied to the substrate is left on the top side of the substrate. A contact layer for contacting a cooling body is applied to a bottom side of the substrate. It is not explicit from US 2014/0 204 533 A1 in which region of the bottom side the contact layer is applied to the bottom side.
A semiconductor module is known from US 2010/0 302 741 A1 which comprises a substrate made from an electrically insulating material. A structured metal layer, via which at least one electrical component is contacted, is applied to a top side of the substrate. The structured metal layer is applied to the substrate only in a central region of the substrate such that an edge region surrounding the central region and in which the structured metal layer is not applied to the substrate is left on the top side of the substrate. A contact layer for contacting a cooling body and which is situated opposite the structured metal layer is applied to a bottom side of the substrate, in the central region and also slightly beyond it.
A semiconductor module is known from US 2013/0 056 185 A1 which comprises a substrate made from an electrically insulating material. A structured metal layer, via which at least one electrical component is contacted, is applied to a top side of the substrate. The structured metal layer is applied to the substrate only in a central region of the substrate such that an edge region surrounding the central region and in which the structured metal layer is not applied to the substrate is left on the top side of the substrate. A contact layer for contacting a cooling body and which is situated opposite the structured metal layer is applied to a bottom side of the substrate. The contact layer appears to extend over the whole bottom side.
The semiconductor modules can, within the scope of the present invention, in particular take the form of power semiconductor modules and comprise, as an electrical component, a power semiconductor, for example an IGBT or a similar component, for example a power MOFSET. Semiconductor modules of this type can be used, for example, in electric cars for switching the energy supply of traction motors. The semiconductor modules can also comprise, as an electrical component, for example a power LED or a resistor.
Within the scope of producing the semiconductor module, pressure is often exerted on the top side of the substrate in a substep by means of a pressing tool. The pressure on the top side is often exerted by the pressing tool via a flexible compensatory material. At the same time as the pressure is exerted, the substrate is held on its bottom side by means of a holding element. Exposure to an elevated temperature, for example in a sintering process, often also takes place in conjunction with the exertion of the pressure.
Because the substrate protrudes beyond the structured metal layer, as part of the abovementioned substep compressive forces are also exerted on the edge region. If the contact layer is applied to the bottom side of the substrate only in the central region, considerable bending forces are often exerted on the transition between the central region and the edge region. In particular because of the high brittleness of the substrate which often exists, this can result in the substrate fracturing. The bending forces can also cause tears in the substrate which, although they may not be noticed initially, later cause premature failure of the semiconductor module.
It is conceivable to design the form of the holding element in such a way that its side facing the bottom side of the substrate has an elevated portion in the edge region such that the holding element supports the substrate not only in the region of the contact layer but also in the edge region. However, this requires a special design, adapted to the respective substrate, of the holding element. This procedure is inefficient in particular in the case of small production runs. Furthermore, in this case the substrate must be positioned precisely relative to the holding element. It is furthermore difficult to manufacture the substrate with the precision required for such a design of the holding element. For example, the thickness of the contact layer can thus be subject to variations from substrate to substrate.
It is furthermore conceivable to design the substrate accordingly with a thickness such that the bending forces remain within the tolerance range. Owing to the greater thickness of the substrate, however, in this case the thermal resistance of the substrate increases such that it is more difficult to reduce the heat of the semiconductor element.
It is furthermore known from the prior art to extend the contact layer over the whole bottom side. By virtue of this procedure, elevated bending stresses owing to the processing pressure are avoided during the production of the semiconductor module. However, on the one hand, air gaps which are required for reliable operation are reduced. Furthermore, the material from which the contact layer is made generally has a different coefficient of thermal expansion from the substrate. When there is a change in temperature, which is inevitable during operation, this results hi a bimetallic effect and hence in warping of the semiconductor module. Such warping can result, for example, in a reduced contact surface area with a cooling body and hence in a reduced cooling of the semiconductor module. In an extreme case, the warping can even cause the substrate to fracture. Other effects such as, for example, pumping of auxiliary or operating materials such as, for example, a heat-conducting paste can also occur.